The present invention relates to an aqueous alkaline processing liquid suitable for use in silver halide photography, more particularly for use in silver complex diffusion transfer reversal processing.
The constituents of a typical developer solution for the development of photo-exposed silver halide emulsion layer materials are a developing agent, alkali, preservative and restrainer acting as antifoggant. The concentrations and the types of constituent have a marked effect on the behaviour of the developer from which is expected, especially in the field of professional photography such as graphic art photography, that reproducible development results are obtained.
Problems encountered with regard to the obtaining of reproducible development results are for a great deal due to the contact of the developer solution with the atmosphere. From the atmosphere oxygen and carbon dioxide enter the developer solution whereby reducing power and alkalinity of the developer decrease.
It has therefore been a main concern to inhibit aerial oxidation and to decrease as much as possible the take up of carbon dioxide that lowers the alkalinity of the developer. In a particular case the aerial oxidation of the developing agent(s) is prevented by incorporating them in non-alkaline conditions in the photographic material itself and to rely in the processing on an alkaline processing liquid, called activator liquid, originally free from developing agent(s).
The aerial oxidation of the developing agent(s) is effectively counteracted by the presence of sulphite ions originating e.g. from sodium sulphite that acts also as alkalinity providing substance.
Suitable developing agents for the exposed silver halide are e.g. hydroquinone and 1-phenyl-pyrazolidine-3-on developing agents as well as p-monomethyl aminophenol .
The alkaline processing solution usually contains sufficient alkaline substances to bring the pH above 10, e.g. sodium hydroxide, sodium carbonate, borax, tertiary sodium phosphate. lithium hydroxide and amines, particularly alkanolamines.
It is not of common practice to use alkanolamines in processing solutions for the classical silver halide photography. In the silver complex diffusion transfer reversal process, called hereinafter DTR-process, said compounds have been introduced already commercially. Liquid processing formulations for use in the DTR-process containing amines and alkanolamines are described e.g. in U.S. Pat. Nos. 2,702,244, 4,568,634 and 4,632,896 and GB 2 159 968.
Tertiary alkanolamines having a pKa value higher than 8.5 and their use in the DTR-process are described in Research Disclosure, July 1987, item 27939 in which it is made clear that alkanolamines and more particularly tertiary alkanolamines as alkali providing substances have a fairly low CO.sub.2 -absorption.
In the processing of photographic silver halide emulsion materials preference is given to a processing liquid which provides a broad temperature latitude and high development rate. By temperature latitude is understood the temperature range wherein an almost high quality of image results is obtained. A particularly good temperature latitude means the production of almost the same image quality in a temperature range of 5 to 40.degree. C. Further the processing liquid should show a broad development latitude by which is understood that the processing liquid withstands very well environmental influences, e.g. the influence of oxygen and carbon dioxide of the air and the influence of the contact with the photographic material to be developed. Development rate concerns the reaction rate wherein a certain silver image density is built up in the photo-exposed silver halide emulsion material in classical silver halide halide photography or in an image-receiving material applied in the silver complex diffusion transfer reversal process.
In practice not all requirements set forth for a developer can be fulfilled simultaneously and therefore it is desirable to have at one's disposal a processing liquid offering an optimized relationship between temperature latitude, development latitude and development rate. It has always been one of the objectives in classical silver halide photography and particularly in DTR-processing to shorten processing times. For the latter purpose it is particularly important that the processing liquid can penetrate rapidly into the hydrophilic colloid layer containing the developable silver halide grains and when applying DTR-processing likewise into the development nuclei containing image-receiving layer so that take-up of processing ingredients is as high as possible in order to have a very rapid and very intense deposit of silver thus forming an image with high optical density and steep gradation suited for halftone reproduction.
The DTR-process initially intended for office copying purposes has found now wide application in the graphic art field, particularly in the production of halftone (screened) prints from continuous tone originals.
The principles of the silver complex diffusion transfer reversal process, have been described e.g. in U.S. Pat. No. 2,352,014 and in the book "Photographic Silver Halide Diffusion Processes" by Andre Rott and Edith Weyde--The Focal Press--London and New York (1972).
In the DTR-process non-developed silver halide of an information-wise exposed photographic silver halide emulsion layer material is transformed with a so-called silver halide solvent into soluble silver complex compounds which are allowed to diffuse into an image-receiving element and are reduced therein with a developing agent, generally in the presence of physical development nuclei, to form a silver image having reversed image density values with respect to the silver image obtained in the exposed photographic material.
The silver halide solvent, mostly sodium thiosulphate, may be supplied from the non-light-sensitive image-receiving element as mentioned above, but it is normally at least partly already present in the alkaline processing solution.
It has been established experimentally (see e.g. the above mentioned Research Disclosure) that DTR-processing solutions containing alkanolamines and more particularly tertiary alkanolamines as alkalinity source offer the advantage of having a comparatively low carbon dioxide absorption and consequently provide a better pH stability and more equal reaction kinetics to the processing solution.
Unfortunately when using alkanolamines the speed of silver image formation is normally not as high as is obtained with inorganic alkali processing solutions containing inorganic alkali providing pH values above 13.